The invention belongs to the field of traffic controls, and more specifically, to the control of road faring vehicle traffic in connection with emergency vehicle traffic.
Whenever an emergency vehicle is traveling under conditions of urgency, the problem of passing through busy street intersections represents a dangerous problem to both the emergency vehicle and to the general traffic at or in the vicinity of the intersection. The problem has become especially severe in recent years when many drivers travel in air conditioned cars with their windows rolled up and often with the radio turned on so that they may be unable to hear the siren of an approaching emergency vehicle. Many serious accidents happen each year as a result of collisions between emergency vehicles and other traffic. In heavy city traffic there is still another problem in relation to the travel of emergency vehicles. As an emergency vehicle approaches a busy intersection and some of the drivers respond to the siren and pull to the curb and halt, as required, busy intersections become filled with vehicles standing still and often completely blocking the progress of the emergency vehicle. Many inventors have in the past sought to devise practical solutions to these problems.
J. O. D. Shepherd, U.S. Pat. No. 2,355,607 issued August, 1944 discloses a system providing radio transmitters mounted on emergency vehicles that radiate a signal that is detected by direction sensitive receivers at the traffic signals and sets the signals such as to admit the emergency vehicle.
F. C. Campana et al, U.S. Pat. No. 3,257,641 issued June, 1966 also discloses a system where a vehicle-mounted radio transmitter sets traffic signals to a special emergency light condition that halts all other traffic.
J. C. Lesher, U.S. Pat. No. 3,247,482, issued April, 1966 discloses a system where an emergency vehicle-mounted radio transmitter broadcasts simultaneously two subcarrier signals which prevent interference of two vehicles simultaneously attempting to control the traffic lights.
Other inventors have disclosed systems that employ sonic or light microwave radio signals in order to control the traffic lights.
H. G. Malach, U.S. Pat. No. 3,881,169, issued April, 1975 discloses a system where each intersection has sonic receivers tuned to certain sound frequencies transmitted by an approaching emergency vehicle, so as to direct the traffic lights to guide the vehicle through the intersection.
L. L. Rose, U.S. Pat. No. 4,016,532 issued April, 1977 discloses a system in which an emergency vehicle mounted transmitter sends a coded signal to a receiver at the intersection where it causes the traffic signal at the intersection to turn to steady red in all directions.
E. Elmasian, U.S. Pat. No. 4,135,144, issued January, 1979 discloses a system in which a radio transmitter mounted in the emergency vehicle causes a receiver at the signal to initiate a light signal sequence that causes the signal to first send flashing red in all directions before turning steady red in all directions.
It appears that none of the systems of the prior art have completely solved the problem of coordinating and controlling traffic so as to accommodate an emergency vehicle in transit since none have gained wide acceptance.
The main problems, it has been found, reside in the fact that city intersections are often very complex in their physical layout and often several intersections are mutually interacting as heavy traffic flows from one traffic direction to another through such inter-related busy intersections. Additionally, the pattern of traffic flow often changes during the day, such that morning rush hour traffic, for example is different from evening hour rush traffic.
The present invention overcomes these problems by providing a two-way interactive encoded communications link between signal controls at an intersection and emergency vehicles, wherein vehicle-mounted communications apparatus transmits, from an approaching emergency vehicle, a digitally encoded message to communications and control apparatus associated with a single traffic intersection or with complicated groups of intersections, that transmits to the control apparatus the identity of the vehicle followed by the desired route through the intersection. The control apparatus at the intersection, in response, inserts the request into an electronic memory bank, residing at the control apparatus, or associated therewith, which in turn provides one of a number of preselected optimal patterns for that intersection, so that the traffic control quickly may clear all traffic lanes to be used by the emergency vehicle instead of blocking them with stalled traffic. The traffic control additionally returns a confirmation code to the emergency vehicle that tells the driver that his request has been received and that he can safely proceed through the intersection.